Multi-die packaging is common in power converters in which Metal Oxide Semiconductor Field Effect Transistors (MOSFETs, which can have a doped polysilicon gate, generally referred to herein as simply FETs) which function as switching transistors are included. Motivations for multi-die packaging as opposed to a single monolithic integrated circuit (IC) solution include both performance and cost.
A conventional power converter package includes a lead frame having a first FET die and a second FET die in a side-by-side or lateral mounting arrangement on a common plane with a controller (or driver) die that is connected via bond wires between conductive pads on the controller die and to contacts on the respective lead frame portions, and by bond wires connected to various contact pads on the FETs. A first clip (also known as a strap), typically formed from copper in ribbon form, is in electrical and thermal contact with the upper surface of the second FET die and a second clip is in electrical and thermal contact with the upper surface of the first FET die. The first clip may be L-shaped and include a columnar portion that is in contact with a contact pad of the lead frame. The second clip is similarly shaped and is in contact with another portion of the lead frame. In typical power converter operations, the clips serve as current carrying conductors as well as heat sinks. This structure is typically encapsulated in a thermoset-based mold compound to define an IC circuit package.
The conventional lateral power converter package is generally thin, but has a foot print (e.g., 5 mm×7 mm) that may be too large for some applications. Moreover, parasitics (inductance and resistance) resulting from long bond wire connections may adversely limit performance including the frequency response (e.g., ringing) and maximum frequency performance. New solutions that minimize the area of power converter package while also providing improved performance are needed for applications including, but not limited to, highly dense servers, set-top boxes, industrial equipment, and notebook computers.